1. Field of the Invention
The present invention relates to optical connectors and more specifically to an optical connector plug, a plug frame and a plug holder comprising the plug, and a method for assembling the plug.
2. Description of Related Art
When performing maintenance or operation for optical transmission equipment and the like, optical fiber cables in the input/output sections of the equipment must be connected and disconnected. A variety of optical connectors are used to enable such connection and disconnection to be performed easily.
A conventional SC type optical connector (hereinafter “SC connector”), in other words, an F04 type single fiber optical connector regulated according to JIS C 5973, and its method of assembly will now be described.
The conventional SC connector comprises an SC connector plug fixed to an end of an optical fiber cable and an SC connector adapter that enables the plug to be readily attached and detached.
FIG. 1 is a longitudinal cross-sectional view of a conventional SC connector plug 100. FIG. 2 is a cross-sectional view along the line II—II of FIG. 1, with the outer housing 102 described subsequently omitted in FIG. 2.
In the case of the optical fiber cable secured to the plug 100, an end of the optical fiber FB1 is secured and supported by a ferrule FE1 shown in dash-dot lines. A cylindrical flange FL1 is secured at the rear end FE2 of the ferrule FE1. Grooves FL2 are formed around the flange FL1 to restrict rotation of the flange FL1 around the central axis thereof.
As shown in FIG. 1, the plug 100 has an outer housing 102 that engages with an adapter (not shown) to couple the plug 100 to the adapter. The housing 102 forms the external shape of the plug 100. A protrusion (not shown) is formed around the outer periphery of the outer housing 102. When the plug 100 is inserted in the adapter, the plug 100 is positioned by means of this protrusion.
A plug frame 104 is arranged at the front end of the outer housing 102 (the end closest to the adapter to be connected, i.e., the left side in FIG. 1). The plug frame 104 is located adjacent the end 100A of the plug 100.
The plug frame 104 comprises a cavity 104A for accommodating the ferrule FE1, and a cavity 104B located at the end of plug frame 104A adjacent the base or end 100B of the plug 100. Cavity 104B accommodates the flange FL1 and receives and connects with the engaging end part 106A of a plug holder 106, described hereinafter.
The plug frame 104 accommodates the ferrule FE1 such that the axis of the ferrule FE1 is positioned along the lengthwise direction or longitudinal axis of the outer housing 102. The respective axes of the cavity 104A and the cavity 104B are substantially coincident. The internal diameter of the cavity 104B is larger than the smallest diameter 104F of the cavity 104A, adjacent to the cavity 104B. The cavity 104B is aligned and connected with the cavity 104A and together with the cavity 104A, forms a through bore in plug frame 104.
The plug frame 104 further comprises a ferrule positioning part or shoulder 104C for positioning the ferrule FE1 along the axial direction of the plug 100. The ferrule positioning part 104C is an annular surface connecting the cavity 104A with the cavity 104B, and is in contact with the surface of flange FL1 facing the end 100A of the plug 100.
Protrusions 104D, which protrude toward the center axis of the cavity 104B and engage the grooves FL2 of the flange FL1, are formed on the interior surface of the cavity 104B at the end thereof adjacent the cavity 104A. The protrusions 104D facilitate positioning the ferrule FE1 and flange FL1 such that the ferrule FE1 and flange FL1 cannot rotate around the axis of the ferrule FE1.
More specifically, four grooves FL2 are provided around the external surface of the flange FL1 at equi-angularly spaced (90°) locations in relation to the axis of the flange FL1, while four protrusions 104D that engage the grooves FL2 are provided around the interior surface of the cavity 104B at equi-angularly spaced (90°) locations in relation to the axis of the cavity 104B. Thus, the angular position of the ferrule FE1 and flange FL1 in relation to the axis of the plug 100 can be changed in 90° increments.
In the outer housing 102, a plug holder 106 is disposed at the rear end of the plug frame 104 (i.e., at the right end of the optical fiber cable as viewed in FIG. 1).
The plug holder 106 comprises an engaging part 106A at the front end thereof that engages in the cavity 104B of the plug frame 104. The plug holder 106 further comprises a spring housing cavity 106B disposed at the front end of the plug holder 106 and a through bore 106C in communication with the spring housing cavity 106B which extends along the longitudinal axis of the plug holder 106. The optical fiber FB1 runs through the through bore formed by the spring housing cavity 106B and the through bore 106C.
The internal diameter of the spring housing cavity 106B is greater than that of the through bore 106C. An annular surface 106D that connects the spring housing cavity 106B and the through bore 106C forms a bearing surface for compressing a compression spring 108.
The compression spring 108 disposed between the bearing surface 106D and the flange FL1 biases the flange FL1 to urge it into contact with the ferrule positioning part or annular surface 104C of the plug frame 104.
The plug holder 106 is inserted into the plug frame 104 and is secured therein by coupling a connecting claw 106E of the plug holder 106 with an engaging cavity 104E formed in the plug frame 104.
According to the above configuration, inside the plug 100, the end of the ferrule FE1 is positioned adjacent the end 100A of the SC connector plug 100 and the flange FL1 and ferrule FE1 are positioned such that the axis of the ferrule FE1 extends in the longitudinal direction of the plug 100.
As described, the ferrule FE1 and flange FL1 cannot rotate axially around the axis of the ferrule FE1, but can move somewhat in the axial direction of the plug 100 in relation to the plug frame 104. That is to say, as the flange FL1 is biased by the compression spring 108 into contact with the ferrule positioning part or surface 104C, the ferrule FE1 and flange FL1 are unable to move in a direction toward the end 100A of the plug 100, but due to the resiliency of the compression spring 108, the ferrule FE1 and the flange FL1 can move in the opposite direction, that is, toward the base 100B of the plug 100.
The inner diameter of the narrowest part 104F of the cavity 104A of plug frame 104 is somewhat larger than the outer diameter of the ferrule FE1. The inner diameter of the cavity 104B is also somewhat larger than the outer diameter of the flange FL1, and thus the ferrule FE1 and flange FL1 can move transversely somewhat, that is, perpendicular to the lengthwise direction of the plug 100.
The parts holding an optical fiber cable in the conventional SC connector plug 100 will now be described.
An optical fiber cable comprises an optical fiber FB1 as described above, an interstitial filler (not shown) made of aramid fiber covering the optical fiber FB1, and a sheath (not shown) covering around the outside thereof.
In the outer housing 102, a cylindrical tubular-shaped filler caulking ring 110 for holding the interstitial filler of the optical fiber cable is disposed surrounding the rear end of the plug holder 106. The end of the interstitial filler is inserted between the filler caulking ring 110 and the plug holder 106, and secured therebetween by caulking the filler caulking ring 110.
In the outer housing 102, a cylindrical tubular-shaped sheath caulking ring 112 for holding the sheath of the optical fiber cable is also disposed surrounding the rear end of the filler caulking ring 110. The end of the sheath is inserted between the sheath caulking ring 112 and the filler caulking ring 110, and secured therebetween by caulking the sheath caulking ring 112.
In addition, in the outer housing 102, a boot 114 for protecting and covering the optical fiber is disposed around the filler caulking ring 110 and sheath caulking ring 112.
As the end of the optical fiber FB1 is inserted into the through bore provided in the ferrule FE1 and adhered therein, the optical fiber FB1 extends from ferrule FE1 to the rear end of the plug holder 106, the optical fiber FB1 covered in the interstitial filler extends from the rear end of the plug holder 106 to the rear end of the filler caulking ring 110, and the optical fiber cable extends from the rear end of the filler caulking ring 110.
The SC connector 100 can be attached or detached simply by insertion in or removal from an SC connector adapter. More specifically, when the plug 100 is pressed into the adapter, a connecting claw (not shown) provided in the adapter is pushed open by the outer housing 102 of the plug 100. As the plug 100 is pushed farther into the adapter, the connecting claw engages with the protrusion of the outer housing 102 and is locked in place thereby such that the plug 100 is firmly connected to the adapter.
Further, holding the outer housing 102 and pulling the plug 100 away from the adapter has the effect of urging the connecting claw open as the outer housing 102 slides out in relation to the adapter, releasing the lock, such that further pulling on the plug 100 enables the plug 100 to be removed from the adapter.
FIG. 3 is a diagram showing the steps for assembling the conventional SC connector plug 100 on an optical fiber cable.
At step S101, a part of the components comprising the plug 100 is passed through with the optical fiber cable. More specifically, the optical fiber cable passes in order, through the boot 114, the sheath caulking ring 112, the filler caulking ring 110, the plug holder 106 and the compression spring 108.
At step S103, pre-processing of the end of the optical fiber cable is performed. This involves the process of exposing the interstitial filler at the end of the optical fiber cable and the process of exposing the optical fiber FB1.
At step S105, the optical fiber FB1 is passed through the flange FL1, through the through hole of ferrule FE1 and is positioned and adhered in the ferrule FE1 such that the tip end of the optical fiber FB1 protrudes somewhat from the through hole of the ferrule FE1. In addition, the flange FL1 is press fitted and secured to the ferrule FE1.
At step S107, the tip of the optical fiber FB1 protruding slightly from the through hole of the ferrule FE1 is cut off.
At step S109, the ferrule FE1 and flange FL1 are inserted into the plug frame 104 and, together with the plug holder 106 and the compression spring 108, are passed through with the optical fiber in advance and inserted into the cavity 104B of the plug frame 104; thereby assembling the plug frame 104, the plug holder 106, the ferrule FE1 and flange FL1 and the compression spring 108.
At step S11, the filler caulking ring 110 is caulked, fixing the interstitial filler of the optical fiber cable, and the sheath caulking ring 112 is caulked, fixing the sheath of the optical fiber cable.
At step S113, the filler caulking ring 110 and sheath caulking ring 112 are covered with the boot 114, and the boot 114 is fixed to the plug holder 106.
At step S115, the plug holder 106 and the plug frame 104 are inserted in the outer housing 102 and secured therein.
At step S117, the end face of the ferrule FE1 positioned at the end 100A of the plug 100 is ground, together with the end face of the optical fiber FB1 secured in the ferrule FE1.
At step S119, these ground end faces are inspected.
At step S121, the assembled plug 100 is attached to an adapter in an inspection device to conduct an inspection of the performance, such as the condition of optical connectivity.
At step S123, if favorable results are obtained from the performance inspection (step S121), the assembly is complete. If the results are not satisfactory, e.g., because the core of the optical fiber FB1 is shifted from center of the ferrule FE1 such that the optical fiber FB1 core is eccentrically positioned, the next step is to proceed to step S125, in which the ferrule FE1 is rotated 90° in relation to the plug frame 104 and the performance inspection of step S121 is performed again. This latter step (step S125) is repeated until favorable results are obtained in step S123.
A conventional FC type optical connector (FC connector), that is to say, an F03 type single fiber optical connector regulated according to JIS C 5970 will now be described.
This conventional FC connector comprises an FC connector plug secured at an end of an optical fiber cable and an FC connector adapter that enables the plug to be readily attached and detached.
FIG. 4 is a longitudinal cross-sectional view of a conventional FC connector plug 200. FIG. 5A is a cross-sectional view along the line VA—VA of FIG. 4, and FIG. 5B is a cross-sectional view along the line VB—VB of FIG. 4. To enable the configuration to be understood more easily, FIG. 5A shows only a plug frame 204 and a coupling ring 250, while FIG. 5B shows only a plug holder 206.
The FC connector plug 200 has a coupling nut 202 instead of the outer housing 102 of the SC connector plug 100. A further point distinguishing the plug 200 from the plug 100 is that the plug holder 206 is secured to the plug frame 204 by a screw connection. In all other respects, the FC connector plug 200 is essentially the same as the SC connector plug 100.
The plug 200 has a cylindrical plug frame 204 supporting a ferrule FE1 and flange FL1 in the same manner as the plug frame 104. A plurality (six as shown in FIG. 5A) of substantially the same shape protruding parts 204A are provided at substantially equi-angular intervals in a circumferential direction, around the intermediate part of the plug frame 204.
A coupling ring 250 engages around the outer periphery of the plug frame 204. A plurality (six as shown in FIG. 5A) of substantially same the shape protruding parts 250A are provided at substantially equi-angular intervals in a circumferential direction, at the rear end of the coupling ring 250.
The protruding parts 250A of the coupling ring 250 and coupling grooves formed between the protruding parts 204A of the plug frame 204 engage mutually together. Further, the protruding parts 204A of the plug frame 204 and the coupling grooves formed between the protruding parts 250A of the coupling ring 250 also engage mutually together. In this way, the coupling ring 250 cannot rotate in relation to the plug frame 204.
At the front end of the coupling ring 250, an engaging part 250B is provided to engage with a coupling groove formed in the adapter. When the plug 200 connects to the adapter as the engaging part 250B engages with this coupling groove in the adapter, the plug frame 204 or the ferrule FE1 supported by the plug frame 204 cannot rotate in relation to the adapter.
The plug frame 204 is surrounded by a cylindrical coupling nut 202. The coupling nut 202 provides a ring-shaped engaging part 202A around the inner circumferential surface of the middle part of coupling nut 202. The engaging part 202A contacts the protruding parts 204A of the plug frame 204 to prevent the coupling nut 202 from coming away from the plug 200 toward the front end thereof.
Around the inner surface of the front end of the coupling nut 202, a screw connecting part 202B is provided to screw together with a screw connecting part of an adapter (not shown). By screw connecting to the screw connecting part of the adapter, the screw connecting part 202B enables the plug 200 to be connected to the adapter.
In the intermediate part of the plug holder 206, an edge 206A with flats (FIG. 5B) is provided to be used for rotating the plug holder 206 with a spanner wrench when the plug holder 206 is screw connected to the plug frame 204. The edge 206A has an external diameter at the arc-shaped portion in the outer periphery thereof that is slightly smaller than the internal diameter of the through bore of the coupling nut 202.
In the FC connector plug 200, the part holding the optical fiber cable is configured substantially the same as the part holding the optical fiber cable of the SC connector plug 100.
The FC plug 200 operates such that the screw connecting part of the coupling nut 202 and screw connecting part of the adapter are mutually screw connected together, thereby enabling attachment to the adapter. Further, the plug 200 can be removed from the adapter by releasing the screw connection of the screw connecting part of the coupling nut 202 and the screw connecting part of the adapter.
FIG. 6 shows the steps for assembling the conventional FC connector plug 200 to an optical fiber cable. The steps are substantially the same as those for assembling the conventional SC connector plug 100 to an optical fiber cable and, thus, need not be described in further detail herein.
At step S221, if favorable results are not obtained from the performance inspection because the core of the optical fiber FB1 is shifted from center of the ferrule FE1, the next step, step S223 is proceeded to, in which the plug frame 204 and the coupling ring 250 are disengaged, rotated and then reengaged. The performance inspection is performed over again at step S221, with the attachment angle of the plug frame 204 in relation to an adapter of a testing device, being changed, for example, in 60° increments.
The optical connector disclosed in Japanese Unexamined Patent Publication No. 4-69369 comprises a plug secured to an end of an optical fiber cable and an adapter enabling this plug to be readily attached and detached in the same manner as applies with respect to an SC connector and an FC connector. The plug and adapter disclosed in that published application are connected by a bayonet connection.
With the plug of the optical connector, the ferrule can be positioned non-incrementally in relation to the plug, i.e., at any desired rotational angle. Accordingly, if favorable results are not obtained from the performance inspection, e.g., because the core of the optical fiber is shifted from center, the performance inspection is re-performed after the ferrule is non-incrementally rotated to any desired attachment angle in relation to the plug, enabling determination of the position that results in the minimum optical connection loss.
The optical connector disclosed in Japanese Unexamined Patent Publication No. 2002-6174 comprises a plug for a readily attachable/detachable optical connector in an SC connector adapter. Inside the plug frame of the plug, a flange coupling ring is provided, the angle of rotation of which in relation to the plug frame can be readily changed. In the flange coupling ring, an engaging part is provided to engage with a flange groove secured to the ferrule.
Rotating the flange coupling ring, when the engaging part of the flange coupling ring engages with the flange groove, rotates the ferrule and the optical fiber secured to the ferrule. In this way, the position of the fiber can be determined in relation to the plug to improve the connective efficiency of the optical connection when the plug is connected to the adapter.
With respect to the conventional SC connector plug 100, the attachment angle around the axis of the ferrule FE1 in relation to the plug 100 can only be changed in 90° increments. Moreover, with respect to the conventional FC connector plug 200, the attachment angle around the axis of the ferrule FE1 in relation to the plug 200 can only be changed in 60° increments.
Thus, the attachment angle around the axis of the ferrule FE1 in relation to the plug can only be adjusted in certain gradations and finer adjustments cannot be made. Accordingly, there are cases when it is not possible to alleviate the positional drift between the core of an optical fiber FB1 supported by a plug and the core of an optical fiber that is connected thereto, in order to reduce connection loss.
The optical connector disclosed in Japanese Unexamined Patent Publication No. 4-69369 allows the attachment angle around the axis of the ferrule in relation to the plug to be non-incrementally changed, however, the plug of this connector employs a bayonet type as the means of coupling the plug to the adapter, so connection is only possible to specific adapters. Accordingly, the problem arises that this plug cannot be coupled with a conventional SC connector adapter or a conventional FC connector adapter.
The optical connector disclosed in Japanese Unexamined Patent Publication No. 2002-6174 also allows the attachment angle around the axis of the ferrule in relation to the plug to be non-incrementally changed. However, a problem arises in the number of parts that must be employed, as it is necessary to provide a flange coupling ring inside the plug frame in order to rotate the ferrule. Further, in order to rotate the flange coupling ring to make the ferrule rotate, it is necessary to provide an opening in the plug frame and insert an elongate special tool from the opening. This makes adjusting the rotational angle of the ferrule in relation to the plug difficult.